Chartwell Managing Agents and Trenwick International (TIL), both part of the Trenwick Group, are restructuring their UK operations.
The companies said they will combine some of their underwriting teams.
TIL's professional indemnity insurance and financial institution teams will move to Chartwell Syndicate 839.
Executive vice president at Trenwick Paul Tester said the move would make Chartwell one of the largest financial institution underwriters in the London Market.
There are also plans for TIL, which specialises in low hazard, smaller risk liability business, to grow its book through the addition of Chartwell's team and business employees. Ian Hamilton will head the combined team.
Chartwell and TIL chairman and chief executive Michael Watson said: "Through this reorganisation we will revitalise, refocus and expand London operations."
TIL's international property and casualty reinsurance treaty portfolio will be underwritten at Lloyd's for 2002. The company plans to expand its range of treaty business.
The group said there are no plans for any redundancies.